1. Field of the Invention
The present invention relates to a resistor for driving a motor for an air conditioner blower for use in an air ventilation unit for an automobile in order to control a rotational speed of the blower motor, and more particularly, to an air conditioner blower motor driving resistor in which resistance bodies made of metal thin plates are separated into two or more sheets of resistance bodies and stacked over one after another together with insulation plates, and a temperature fuse is externally disposed.
2. Description of the Related Art
Various types of resistors for driving a motor for an air conditioner blower are known.
FIG. 1 is a perspective view showing an example of a conventional resistor for driving a motor for an air conditioner blower. FIG. 2 is an exploded perspective view of the FIG. 1 conventional resistor. FIG. 3 is a perspective view showing another example of a conventional resistor for driving a motor for an air conditioner blower. FIG. 4 is an exploded perspective view of the FIG. 3 conventional resistor. FIG. 7C illustrates a resistance body of a single plate structure for use in a conventional air conditioner blower motor driving resistor. FIG. 12B schematically shows a resistance body realized in a conventional air conditioner blower motor driving resistor.
Referring to FIGS. 1 through 4, 7C and 12B, a conventional air conditioner blower motor driving resistor includes a connector 20 for connecting to an air ventilation unit and a resistor 10 having a resistance body 11.
The resistor 10 includes a thermal radiator 13 for emitting heat of the resistance body 11, a cover member 14 for covering the resistor 10, and insulation plates 12 installed at both sides of the resistance body 11 in order to insulate the resistance body 11, in which a soldering portion 30 being an overheat prevention unit is soldered and connected between the lower terminals.
The resistance body 11 in the resistor 10 includes a common terminal 21 and three select terminals 22, 23 and 24, in which a resistance circuit is formed so that respectively different resistance values exist between the terminals 22, 23 and 24.
Hereinafter, a resistor between the common terminal 21 and the first select terminal 22 is denoted as R3, a resistor between the first select terminal 22 and the second select terminal 23 is denoted as R2, and a resistor between the second select terminal 23 and the third select terminal 24 is denoted as R1. Also, the rotational speed of the blower motor is called a first step speed, a second step speed and a third step speed from the lowest speed.
That is, if the common terminal 21 and the third select terminal 24 are selected, the resistance value becomes R1+R2+R3. As a result, since the resistance value becomes the largest, the rotational speed of the blower motor becomes the lowest speed, that is, the first step speed. If the common terminal 21 and the second select terminal 23 are selected, the resistance value becomes R3+R2. As a result, the rotational speed of the blower motor becomes the second step speed. If the common terminal 21 and the third select terminal 22 are selected, the resistance value becomes R3. As a result, the rotational speed of the blower motor becomes the three step speed which is the highest speed.
In the case of the conventional resistance body, the respective resistance values are formed on only a single metal thin plate. As a result, as shown, the line width of the resistance body 11 is very narrow and the interval between the resistance circuits is also narrow. Accordingly, the short circuit phenomenon frequently occurs to raise an out-of-trouble. Also, the intensity is lowered to make it difficult to fabricate a resistor.
That is, as shown in FIGS. 7C and 12B, in order to have a resistance value in a limited area, a portion denoted as xe2x80x9caxe2x80x9d has an extremely narrow line width in case of R1. As illustrated in the following equation,
R=xcfx81xc3x97(L/A)[xcexa9]
(R: resistance, xcfx81: specific resistance, A: cross-sectional area, and L: the length of a circuit), since a resistance is proportional with a length, and inversely proportional with a cross-sectional area, a portion xe2x80x9caxe2x80x9d having a cross-sectional area of such a narrow line width can be easily overheated. Accordingly, the resistance value can be varied due to the heat. As a result, the resistance value becomes a resistance value differing from a design resistance value, to thus raise an operational error.
Meanwhile, a heat generated from a resistor circuit will be described with reference to the following equation.
H=0.24xc3x97I2RT[cal]
(I: current, R: resistance, and T: unity time)
A heat generated during operation of a resistor, called a Joule""s heat is proportional with a square of current. As described above, the Joule""s heat is inversely proportional with a cross-sectional area of the circuit. In order to reduce a current density per a unity area, a circuit width should be increased to dissipate the generated heat. This should be reflected on designing and fabricating a circuit and a heat radiator.
That is, as the width of a thin plate forming a resistance circuit is narrower, a possibility of breaking of wires becomes higher. As the width of a thin plate forming a resistance circuit is wider, a possibility of breaking of wires becomes lower. Thus, a structural change necessary for improving the line width of each resistor has been required.
As illustrated in the Table of FIG. 13, an electric power of the resistance in each resistance body is 10.6 W for R3, 18.2 W for R2 and 30 W for R1 in case of a first step speed, 35 W for R3, 60 W for R2 and 0 W for R1 in case of a second step speed, and 140 W for R3, 0 W for R2 and R1 in case of a three step speed. In this case, it can be seen that the electric power at the R1 and R2 sides becomes much smaller than that at the R3 side. In order to thermally radiate the entire resistance body, a thermally radiating structure without considering a heat generating quantity for each resistance body may cause a loss of materials for fabricating components.
In particular, as shown in FIGS. 3 and 4, a cylindrical temperature fuse has been used as an overheat preventive unit in the conventional art. However, since such a resistor structure adopts a structure of soldering and connecting the resistance bodies at the state where the outer upper portion of the cover member is cut, it may cause a short circuit with the inner wall of the thermal radiator. Also, since dispersion of a resistance value R3 is large, the structure of the resistor is complicated, and the fabrication process is difficult, a production cost becomes high and a failure rate level is high.
Also, since a conventional resistance body of a copper-nickle alloy needs a high material cost. It is nearly impossible to be applied as a semiconductor material since dispersion of the resistance value is high. Also, since a temperature characteristic is inferior and a mechanical strength is not good in the processes of the film etching and the resistor assembly.
To solve the above problems of the conventional air conditioner blower motor driving resistor, it is an object of the present invention to provide an air conditioner blower motor driving resistor, in which resistance bodies are separated into a number of metal thin plates and stacked over one after another, to thereby obtain a desired resistance value and reduce volume of the resistor to be more compact, and to thereby secure line widths in resistance circuits and intervals between the resistance circuits in order to reduce a short circuit frequency during overheat and suppress a failure rate.
It is another object of the present invention to provide an air conditioner blower motor driving resistor in which a thermal radiator is minimized and removed in a resistor side having a small amount of electric power proportional with a heat emission amount, and is designed and disposed in a R3 side having a large amount of electric power, in a manner that a thermal radiating structure is not included in a portion having a small amount of heat emission.
It is still another object of the present invention to provide an air conditioner blower motor driving resistor of an iron-nickle alloy which is more excellent and less material cost than a copper-nickle alloy, in which a dispersion of resistance value is low, a temperature characteristic is excellent, and a mechanical strength is excellent in the processes of film etching and resistor assembly, so as to be used as a semiconductor material.
It is yet another object of the present invention to provide an air conditioner blower motor driving resistor capable of assembling an overheat prevention unit externally from a thermal radiator and securing a stability of designing with respect to an assembly structure of a short circuit preventive unit.
To accomplish the above object of the present invention, there is provided a resistor for driving a motor for an air conditioner blower, the air conditioner blower motor driving resistor comprising: a resistor unit obtained by stacking insulation plates and resistance bodies alternately over one after another, in an inner accommodating area while combining protrusions formed along the upper and left and right portions of a resistor cover member forming an accommodating space with a thermal radiator; and a connector unit on the lower portion of which power source terminals are covered with a connector cover member and on the upper portion of which terminals soldered and connected with the resistance bodies stand erect.
Preferably, the resistor unit comprises a first independent resistance body and a second independent resistance body obtained by combining two resistance bodies each having a small resistance value.
Preferably, the resistor unit in the resistor can be formed in a multi-layer, for example, three-layer resistance bodies which are independently separated, respectively.
Preferably, the material of the resistance body in the resistor is an iron-nickle alloy.
Preferably, the air conditioner blower motor driving resistor further comprises a temperature fuse which is short circuited during overheat through the resistance bodies, in order to protect an inner circuit.
In the air conditioner blower motor driving resistor comprising the connector unit and the resistor unit, the resistance bodies are alternately formed in a multi-layer form between the insulation plates.